The present invention relates generally to integrated angular rate and acceleration sensors (“multi-sensors”), and more specifically to a six degree-of-freedom micro-machined multi-sensor device capable of providing 3-axis of acceleration sensing and 3-axes of angular rate sensing.
Micro-machined multi-sensors are known that comprise at least one accelerometer for providing indications of acceleration sensing and angular rate sensing in a single multi-sensor device. A conventional micro-machined multi-sensor, as described in U.S. Pat. No. 5,392,650 issued Feb. 28, 1995 entitled MICRO-MACHINED ACCELEROMETER GYROSCOPE, comprises a pair of accelerometers, in which each accelerometer includes a rigid accelerometer frame anchored to a substrate, and a proof mass suspended from the rigid frame by a plurality of flexures. The micro-machined multi-sensor typically has a single acceleration-sensing axis, and a single rotation-sensing axis perpendicular to the acceleration axis, associated therewith. Further, the micro-machined multi-sensor is typically configured for simultaneously vibrating the proof masses in antiphase along a vibration axis, which is perpendicular to the acceleration and rotation axes.
In the event the conventional micro-machined multi-sensor is subjected to linear and rotational motions while the proof masses are simultaneously vibrated in an antiphase manner, forces of linear and Coriolis acceleration are generated that deflect the proof masses relative to the substrate. The multi-sensor is configured to sense the deflections of the respective proof masses, and to produce corresponding acceleration sense signals having values proportional to the magnitude of the deflection. Because the responses of the vibrating proof masses to linear acceleration are in phase, and the responses of the proof masses to Coriolis acceleration are in antiphase, the linear acceleration components (containing the acceleration sensing information), and the rotational acceleration components (containing the angular rate sensing information), of the sense signals can be separated by suitably adding or subtracting the signals to cancel the rotational or linear components, respectively.
One drawback of the above-described conventional micro-machined multi-sensor is that it typically provides only 1-axis of acceleration sensing, and only 1-axis of angular rate sensing. However, it is often advantageous to provide more than one axis of acceleration sensing and/or angular rate sensing in a single micro-machined multi-sensor device.
A second conventional micro-machined sensor capable of measuring rates of rotation relative to two rotation-sensing axes is described in U.S. Pat. No. 5,869,760 issued Feb. 9, 1999 entitled MICRO-MACHINED DEVICE WITH ROTATIONALLY VIBRATED MASSES. The micro-machined sensor comprises a pair of accelerometers, in which each accelerometer includes a mass in the form of a circular beam suspended over a substrate by a plurality of flexures, and an adjacent pair of acceleration-sensing electrodes. The two rotation-sensing axes associated with the micro-machined sensor are in the plane of the substrate. Further, the micro-machined sensor is configured for rotationally vibrating the circular beams in an antiphase manner, i.e., alternately rotating one circular beam clockwise/counterclockwise while the other beam simultaneously rotates in the opposite direction by substantially the same amount.
In the event the second conventional micro-machined sensor is subjected to linear and rotational motions while the circular beams are simultaneously rotated in antiphase, forces of linear and Coriolis acceleration are generated that deflect the beams relative to the substrate. The acceleration-sensing electrodes sense the deflections of the respective beams, and produce corresponding acceleration sense signals proportional to the magnitude of the deflection and the rate of rotation relative to the rotation-sensing axes. Because the sign of the rotational acceleration components (containing the angular rate sensing information) of the sense signals corresponds to the direction of rotation of the circular beams, the rotational components can be separated from the linear acceleration components of the sense signals by suitably subtracting the signals to cancel the linear components. However, although the micro-machined sensor is capable of providing more than one axis of angular rate sensing, it has drawbacks in that it typically provides no acceleration sensing information.
It would therefore be desirable to have a micro-machined multi-sensor that provides more than one axis of acceleration sensing, and more than one axis of angular rate sensing, in a single multi-sensor device. Such a micro-machined multi-sensor device would avoid the drawbacks of the above-described conventional micro-machined sensor devices.